1. Field of the Invention
The present invention relates to a pH dependent ion exchange material having a carboxyl group, an amino group, and a polyethylene oxide moiety, a solid substrate having the material immobilized on its surface, and a method of isolating a nucleic acid using the material or the solid substrate.
2. Description of the Related Art
pH dependent ion exchange matrices and methods of isolating nucleic acids using them are known. For example, U.S. published patent application No. 2001/0018513 describes a method of isolating a nucleic acid using a material containing an ionisable group which is positively charged at a first pH such that it can be bound to the nucleic acid and releasing the nucleic acid at a second pH which is higher than the first pH. Examples of the material containing an ionisable group include N-2-acetamido-2-aminoethanesulfonic acid (ACES), N-2-acetamido-2-imidodiacetic acid (ADA), N-trihydroxymethyl-methyl-2-aminoethanesulfonic acid (TES) and trihydroxymethylaminoethane (Tris), etc. U.S. Pat. No. 6,310,199 describes a method of isolating a nucleic acid using a pH dependent ion exchange matrix, the matrix comprising a silica magnetic particle and a plurality of first ion exchange ligands, each first ion exchange ligand comprising an aromatic hydrocarbon ring, a spacer covalently attached to the aromatic hydrocarbon ring, and a linker comprising a linker alkyl chain attached to the silica magnetic particle at its first end and attached to the spacer at its second end.
However, since the conventional pH dependent ion exchange materials have a high binding ability to proteins as well as to nucleic acids in a sample, the efficiency of selectively isolating the nucleic acids from the sample is low.
Thus, the inventors of the present invention searched for pH dependent ion exchange materials which can bind strongly to the nucleic acids at a first pH and release the nucleic acids at a second pH in a high ratio, but bind weakly to the proteins, and thus can be used for selectively isolating the nucleic acids from the sample, and discovered a pH dependent ion exchange material according the present invention.